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We prove the #P-hardness of the counting problems associated with various satis-fiability, graph, and combinatorial problems, when restricted to planar instances. and the D P-completeness (with respect to random polynomial reducibil-ity) of the unique satisfiability problems [L. G. Valiant and V. V. Vazirani, NP is as easy as detecting unique solutions, in(More)
We consider the problem of placing a speciied number (p) of facilities on the nodes of a network so as to minimize some measure of the distances between facilities. This type of problem models a number of problems arising in facility location, statistical clustering, pattern recognition, and also a processor allocation problem in multiprocessor systems. We(More)
We study the eecient approximability of basic graph and logic problems in the literature when instances are speciied hierarchically as in 35] or are speciied by 1-dimensional nite narrow periodic speciications as in 58]. We show that, for most of the problems considered when speciied using k-level-restricted hierarchical speciications or k-narrow periodic(More)
We characterize the complexity of a number of basic optimization problems for unit disk graphs speciied hierarchically as in BOW83, LW87a, Le88, LW92]. Both PSPACE-hardness results and polynomial time approximations are presented for most of the problems considered. These problems include minimum vertex coloring, maximum independent set, minimum clique(More)
We present an architecture and prototype implementation for a generic provenance database middleware (GProM) that is based on the concept of query rewrites, which are applied to an algebraic graph representation of database operations. The system supports a wide range of provenance types and representations for queries, updates, transactions, and operations(More)
Energy. The Los Alamos National Laboratory strongly supports academic freedom and a researcher's right to publish; as an institution, however, the Laboratory does not endorse this viewpoint of a publication or guarantee its technical correctness. Abstract. We study the complexity of various combinatorial problems when instances are speciied using one of the(More)